1. Field
The present embodiments relate to methods and systems for calibrating laser intensities sampled by a three-dimensional multi-color laser scanning system. Specifically, the present embodiments relate to methods and systems for determining color values of scanned objects using information obtained from calibrating laser intensities in a three-dimensional multi-color laser scanning system.
2. Description of Related Art
Three-dimensional laser scanning systems are known in the art. For example, U.S. Pat. No. 5,231,470 issued to Koch and U.S. Pat. No. 6,480,287 issued to Lee et al. disclose three-dimensional scanning systems. Furthermore, various color calibration methods are known for other imaging devices, such as printers, copiers and flatbed scanners (e.g., see U.S. Pat. Nos. 5,809,366, 6,840,597 and 6,851,785). However, there currently does not exist an accurate method for calibrating colors in a three-dimensional multi-color laser scanning system.
Object intrinsic color value calculation has been a significant problem in scanning technology. Color values may be 25% off object intrinsic color values in conventional three-dimensional multi-color laser scanning systems. This error becomes even higher when an intrinsic color reflectance (expressed in a range of zero to one) is close to zero or one.
There are various explanations for the lack of accuracy in object intrinsic color calculation in conventional three-dimensional multi-color laser scanning systems. For example, conventional methods assume and implement a linear response between laser intensities and color reflectance, thereby causing a significant error in the calibrated color values, which may be as high as 24% off of true color values. Conventional methods also assume and implement a simple cosine response between laser intensities and reflection angles (angles between surface normal directions and lens detection direction), thereby causing significant over compensation when a reflection angle is near 0 degrees (e.g., 0-20 degrees), and under compensation when a reflection angle is near 90 degrees (e.g., 70-90 degrees). The resultant errors can be as high as 50% off of true color values. Additionally, calibration information in conventional methods is often obtained from scanning a single calibration target, such as a white flat bar, and no other calibration targets. This is often insufficient to establish a reliable correlation between color reflectance and laser intensities.
Accordingly, there is a need for a multi-colored three-dimensional laser scanner system for accurately capturing the intrinsic colors of scanned objects.